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>> Sunday, July 25, 2010

The capsule from Apollo 13

Aron Sora asked [building off my last post]: True, but why is manned space more expensive. Why isn't most of the cost for manned flight contained in radiation hardening and designing for temp. extremes?

Good question. Some of the expensive for human spaceflight is for radiation hardening and redundancy and reliability and thermal extremes. Everything true for a multi-million dollar space craft or rover is even more true a spacecraft carrying people. People forget when even an expensive satellite or probe fails. People remember when humans die in space. Even if the folks at NASA didn't care about the humanity lost (and they care, desperately, about that), the impact to existing programs is devastating.

But the long pole for unmanned missions (this design and testing) is just the tip of the iceberg for manned space exploration. For unmanned, you can make things as small as you can make them, as light as you can make them to perform whatever functions you need, and need only enough propulsion to get them where they need to go.

Manned spacecraft must do all that plus (a) they need environment, food, water, clothing, controls, displays, computer equipment, communication equipment, protection from thermal extremes, vacuum, radiation and g forces, waste control systems (air and other), backup systems and a minimum volume over and above what their body takes up AND (b) they must not only make it there, they must make it back . . . safely.

Whereas a satellite or unmanned rover can be disabled and use no power until put into use, manned vehicles must have power, thermal rejection and environmental systems at all time. They must have thermal protection for reentry and protection from excessive shock forces for landing. Not only do we need all these systems, we must have constant instrumentation of these systems (frequently more instrumentation just for these systems than an unmanned craft would have altogether), primary and backup voice and data communication, controls, equipment or instruments (or why bother with people), and consumables/waste facilities. None of which is required for an unmanned one-way rover. And all of these systems need to be tested, preferably in a flight environment, certified and demonstrated working together to get confidence they will keep people alive.

Making it back is a huge deal as well, as I described here, here and here. It means effectively twice the propulsion in separate stages and systems (with separate fuel systems and control systems for each). It means many times the complexity as doing anything outside low earth orbit requires multiple vehicles working in concert, with duplication of controls and systems. It's such a huge scary difficult deal, the number of unmanned missions that have returned can be counted on one hand.

And, yes, I still think it's worth it, partially because it is so difficult. In fact, it's because it's so difficult that I think it's worthwhile. If we can do that, we have no limits.

1 comments:

Before there exist a human spaceflight, there are hundreds of test flights that are done and that means a lot of money was invested in it. That is one of the reason why a human spaceflight is reall expensive in the first place.